If you asked me for one – just one – nutrition recommendation that would benefit most people, I’d tell you to eat more fiber. Fiber isn’t sexy or new, but it’s the closest we’ve come to a holy grail of health.
What is fiber?
Fiber is a carbohydrate found in many foods. Because it can’t be digested, or broken down and absorbed, it passes through our digestive systems.
There are two main types of fiber: soluble, and insoluble. Just to say it before we get started, you don’t have to count grams of total fibre, or keep a close eye on which type of fiber you get each day. A varied diet naturally has a combination of fibers, and that’s all you need to remember.
Soluble fiber dissolves in water, turning into a gel. It helps to slow the digestion of food, making us feel fuller for longer, and helping to control blood glucose levels. It can bind cholesterol in the small intestine, taking it out of the body.
Soluble fiber is found in high fiber foods like oat bran, barley, psyllium (more on this later), nuts and seeds, dried beans and lentils, and some vegetables and fruit.
Insoluble fiber does not dissolve in water. It helps to increase stool bulk and may improve constipation and promote a healthy digestive system and regular bowel movements. Insoluble fiber is found in the skins of vegetables and fruit, whole grains, and wheat bran.
Net carbs are the total carbohydrates in a food, minus fibre. Because fiber is a carb, total fibre grams are shown under the ‘carbohydrate’ section of food labels. But because fiber is indigestible, separating the fiber grams from the ‘total carbohydrate’ number results in the net carbs amount – basically, the amount of carbohydrate our bodies can absorb.
For people following a low-carb or keto diet, the net carb number of foods is important.
Just to clear this up now, that shirtless carnivore doctor who says that fiber isn’t necessary for health? The preponderance of evidence proves that he’s dead wrong. The very fact that some people out there are going against all of this evidence and saying that we don’t need fiber, is outrageous.
I guess it gets them more clicks and followers.
You may have heard the term ‘resistant starch.’ This is a type of fibre that is undigestible and fermentable, and that feeds our good gut bacteria. Unlike other, more digestible types of starches, resistant starch isn’t absorbed in the small intestine – it ends up in our large intestine, where our good gut bacteria live.
Resistant starch is found in a lot of the foods that we consider to be starches – raw oats, potatoes, beans and lentils, unripe bananas, rice, and pasta. Cooking and cooling potatoes, rice, and pasta actually increases the amount of resistant starch in these foods.
This graphic and paper go into more detail about resistant starch.
Resistant starch was in the media quite a bit a few years back, when it was discovered that cooking and cooling rice decreases its total calories absorbed…because of the increase in resistant starch.
Whole-food sources of resistant starches appear to be more beneficial than those found in supplements.
Benefits of fiber
Fiber and gut health
While exercise, water intake, stress and other factors affect our bowel habits, diet plays a large role! Fiber helps to move waste products through our colon. This in turn, has been shown to reduce constipation. Different types of fiber do this in different ways, including bulking stools, softening stools, supporting healthy microbiome fermentation and causing mild irritation of the colon to increase the motion and release of water – all of which keep us moving!
Fiber appears to be the preferred food for the little bugs in our gut: when we consume fiber and it ends up in our large intestine, our good bacteria feast on it, fermenting it into short chain fatty acids. These SCFAs lower the acidity of our colon, making it more hostile to pathogenic bacteria. Research suggests that SCFA may also lower inflammation and increase gut integrity, play a role in fat metabolism and glucose control, and regulate the immune system and blood pressure.
Fiber and heart health
Type 2 diabetes, and high cholesterol are known risk factors for heart disease, stroke, and other chronic health issues. This means that avoiding or properly managing these conditions, likely will help reduce the chances of health incidents in the future.
That’s the beauty of fiber, it’s not a one trick pony. A number of large, high quality epidemiological studies have shown that increasing fiber intake is associated with a significantly lower chance of developing heart disease, stroke and diabetes, when compared to low fiber diets. In a pooled analysis of more than 185 studies, This benefit was found to be most when consuming more than 25 grams of fiber a day (more on that later).
Fiber and cancer
The same, and other large, reputable studies showed that low fiber diets are associated with an increased risk of some cancer types, including colorectal. Conversely, diets high in fiber have been linked to lower risk of colon cancer. While cancer risks are very complicated, and confounders (other factors that may give us a false signal) can exist in this type of research, the data is quite consistent. There is also developing theories and emerging evidence regarding high fiber diets and links to decreased breast cancer risk.
Fiber and weight loss
Aside from taking longer to digest, and helping us feel fuller for longer, fiber has other benefits for weight loss and maintenance.
Naturally present fiber in some foods like nuts, binds the naturally occurring fats in those foods and inhibits their absorption. For example, when we eat almonds or walnuts, research has shown that we don’t absorb some of the fats in them, because they’re bound in the nut’s fiber.
A recent study in Nature Communications suggests that compared to a low-fiber Western diet, a diet high in fiber not only feeds our good gut bacteria, but also leads to a microbiome-mediated reduction in calories absorbed.
In plain language, the more fiber we eat, the more energy the bugs in our guts use to multiply, and the fewer calories we absorb from that food.
It’s important to understand that replacing the majority of high fiber foods in your diet with fiber supplements isn’t healthy, both physically and emotionally. Food contains necessary compounds for health that fiber doesn’t have, and fiber supplements will not give you the energy or satisfaction that food provides. There is a place for fiber supplements, though.
Does fiber inhibit nutrient absorption?
It can, in particular with iron, calcium, and magnesium. If you’re taking these nutrients in supplement form, it’s best to take them separately.
How much fiber do I need, and where can I get it?
Fiber recommendations are pretty straightforward: 25 grams a day for women, and 38 grams per day for men. but many other guidelines vary by age, whether or not you’re pregnant or breastfeeding, and gender.
Here’s the thing: when it comes to fiber, most of us don’t get anywhere near enough. It’s estimated that most North Americans get about HALF of the recommended daily intake. This has long been a criticism of the highly refined modern ‘Western diet’, and cited as a potential reason for many unfortunate health trends in North America.
High fiber foods: how to increase your fiber intake
In general, eating a varied diet rich in vegetables, fruits, and nuts should get you close enough to what you need without having to track every bite. However, for those who are curious, there are some great charts online you can use as reference.
Here are some high fiber food recommendations:
Avocados are a great source of dietary fiber. They have a neutral flavour, and creamy texture that can be incorporated into many dishes as a fiber boost. Adding half into a smoothie or salad can boost the fiber content by 6-7 grams.
Dried fruits like prunes are a good source, as are nuts and seeds. Toss the dried fruits of choice with some nuts, mix in a little bit of your favourite chocolate, and you have a delicious, high fiber trail mix that packs easily and stores well.
Beans pack a big punch! There’s a reason they have a reputation for keeping you regular – it’s all that fiber. A cup of pinto beans has nearly 15 grams of fiber. Experiment with vegetarian chili – the different beans, vegetable and seasoning combinations give different flavours and textures to keep the food interesting and delicious, all while providing a huge fiber influx. It can be easily frozen and reheated for leftovers, which is perfect for meal prep.
Sprinkle a half cup of seeds, nuts and berries on salads, to give an already important source of fiber a big boost.
A cup of boiled green peas contains 7 grams of fiber and 8 grams of protein. Again, the relatively neutral flavour helps them hide well in casseroles, soups or just as a super fast side at dinner. Mix them with your regular side dish of rice, or throw some on your pasta. They’re quick to boil straight from the freezer.
Add half a cup of lentils to soup stock, let them soften and puree them. This can offer a nice creamy texture while adding little flavour, but a whole whack of fiber. The difference will be hard to notice, and the boost in fiber will be substantial.
For a top-up, you can add fiber supplements to your diet. While this may seem simple, some supplements can be high in sugar. Some fiber supplements can also be limited in one type of fiber.
For example, the active ingredient in Metamucil is psyllium husk, a predominantly soluble fiber, so you’re missing out on some benefits of the insoluble fibres found in many whole foods.
The product doesn’t contain significant quantities of other beneficial vitamins, minerals, proteins and healthy fats – the great things we get from fruits, vegetables, grains and legumes.
Is there such a thing as too much fiber?
There are some health conditions where lots of fiber can be irritating or harmful (some active bowel diseases, anatomic bowel changes, certain medical treatments), and best to heed the advice of your healthcare provider if you’re in this category!
Additionally, if you’re otherwise well, and thinking about increasing the fiber in your diet, rapid increases in fiber intake are associated with excess gas, bloating and cramping.
Adding high fiber foods slowly to help your body adjust, making sure you’re well hydrated, and physically active can all help minimize these issues.
Finally, focusing on just one fiber boosting change may seem easiest, but I always suggest a variety of high fiber foods like fruits, vegetables, legumes and whole grains to give a mix of subtypes of fiber and their respective benefits, and an interesting and varied diet with all sorts of nutrients, flavours, textures and recipe options you won’t get bored of.